Electron discharge devices employing cavity resonators



1959 A. F. PEARCE ETAL 2,901,660

ELECTRON DISCHARGE DEVICES EMPLOYING CAVITY RESONATORS Filed April 7, 1954 FIG.1.

2 4 s 6 E 11 z 16 5 INVENTOE 1.17Pezr 6 2 Sheets-Sheet 1 iww ll fkfoottozz/ 1959 A. F. PEARCE ETAL 2,901,560

ELECTRON DISCHARGE DEVICES EMPLOYING CAVITY RESONATORS 2 Sheets-Sheet 2 F'iled April 7, 1954 FIG. 10.

. .Dolfloottolz/ uLuQm vj Ma Unite ELECTRON DISCHARGE DEVICES ENIPLOYING CAVITY RESONATORS Application April 7, 1954, Serial No. 421,542

Claims priority, application Great Britain April 10, 1953 18 Claims. (Cl. 315-5.32)

This invention relates to electron discharge devices employing cavity resonators.

Frequently in such devices the cavity resonator is in the form of a toroidal body having a central aperture through which a beam of electrons is caused to pass. In these devices the power is usually abstracted from the resonator by means of a loop formed on the end of a co-axial line and projecting into the resonator or by a single slot provided in the wall of the resonator which leads into a waveguide. In order to enable higher powers to be generated, it has been proposed to employ toroidal resonators having an annular gap through which a sheet-like beam of electrons is arranged to pass or in which a hollow cylindrical beam of electrons is caused to pass. With this latter kind of device, since the cavity resonator is larger for a particular frequency compared with a cavity resonator having a central aperture, the resonator has a variety of possible cavity modes. If, therefore, power is fed to or abstracted from the resonator from a single point, as is the practice with cavity resonators which have a central aperture through which the beam passes, there is the danger that the asymmetry which is introduced due to the single output connection may cause the cavity to oscillate in some unwanted mode.

The object of the present invention is to provide an improved device employing a toroidal cavity resonator having an annular gap with a view to reducing the abovementioned disadvantage.

According to the invention there is provided an electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having at least one opening separate from said openings forming said annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode.

In general the preferred or wanted mode is one having no nodes around the periphery of the cavity resonator whereas unwanted modes will have an even number of nodes from two upwards.

The invention may be applied either to the kind of cavity resonator in which a sheet-like beam of electrons is arranged to pass through an annular gap or in which a hollow cylindrical beam of electrons is employed and in either case the energy transferring means may include a coaxial line or a waveguide.

In order that the said invention may be clearly understood and readily carried into effect, it will now be described with reference to the accompanying drawings, in which:

Figure 1 is a view in cross-section of an electron distes Patent charge device in accordance with one embodiment of the invention,

Figures 2, 3 and 4 illustrate portions of the device shown in Figure 1 showing modifications,

Figure 5 is a cross-sectional view through a resonator embodying an alternative form of energy transferring means,

Figure 6 is a view taken along the line 66 of Figure 1 Figure 7 is a cross-sectional view of a device employing a pair of cavity resonators,

Figure 8 is a sectional view illustrating the invention as applied to an electron discharge device employing a hollow cylindrical beam of electrons,

Figure 9 is a sectional view of a modified construction of the arrangement shown in Figure 8, and

Figure 10 is a sectional view of part of Figure 8 illustrating an alternative form of energy transferring means.

As shown in Figure 1 of the drawings, the electron discharge device comprises a toroidal cavity resonator 1 which is in the form of a double-walled cylinder, the inner wall of which is provided with a re-entrant portion 2 in which is formed an annular opening, the re-entrant portion extending into close proximity to an annular opening 3 formed in the other wall of the cylinder. An annular cathode 4 is provided the electron emitting surface of which may be plane or concave as shown, said cathode being carried by a ceramic insulator 5 and being associated with screen electrodes 6 which, when suitably energised, serve to cause electrons emitted from the cathode 4 to be projected in sheet-like form through the gap in the resonator 1 formed by said opening. Surrounding the annular opening 3 is a reflecting electrode 7, which when suitably energised, serves to cause electrons passing through the cavity resonator to be reflected back therethrough so that the device functions as an oscillation generator, the frequency of the generated oscillations depending on the resonant frequency of the resonator 1. Such a device is generally known in the art and it is also known to interchange the positions of the cathode 4 and the reflecting electrode 7.

Devices of the above kind are required to operate in vacuo and accordingly the device is provided with a vacuum tight envelope comprising a cylinder 8 provided with a bottom wall 9 and a top Wall 10, the envelope being made, for example, of steel and suitably welded together in a vacuum tight manner. A pinch for the leads to the various electrodes of the device is indicated at 11. In order to transfer energy from the cavity 1 an odd plurality (i.e. at least three) of apertures 12 .(one of which is shown in Figure l) are formed in the cavity wall and uniformly disposed around the cavity, these apertures being surrounded by a tapered coaxial line 13 which feeds into a circular Waveguide 14 operating on the E0 mode. The tapering of the line 13 is so chosen as to match the impedance of the line 13 to that of the waveguide 14. The inner conductor of the coaxial line 13 is in the form of a cone as shown carried by a disclike support 15 having a central boss 16 which serves to provide a support for the cathode 4 and the screen electrodes 6, as shown. The outer conductor of the coaxial line 13 is provided with a peripheral flange 17 which may be Welded to the top wall 10 of the envelope. The reflecting electrode 7 in the example shown is carried by a ceramic insulator 18 which is suitably secured to the flange 17. The outlet end of the waveguide 14 is closed in a vacuum tight manner by a glass window 19 as is known in the art. With the arrangement shown energy from the resonator 1 is fed via the apertures 12 into the tapered coaxial line 13 and since the apertures 12 are uniformly disposed around the cavity 1, a more uniform loading of the cavity is afforded. In one example, wherethe resonator 1 is designed for operation at a frequency of 10,000 mc./s. seven apertures 12 may be provided. The size of the apertures 12 will be determined by the degree of coupling required to the line 13 and the loading. The apertures 12 may be circular or inthe form'of slots. The more uniform loading of the cavity in accordance with the invention serves to reduce the possibility of the cavity oscillating in an unwanted mode.

If desired, as shown in Figure 2 of the drawings, instead of employing the waveguide 14 the cone forming the inner conductor of the coaxial transmission line may be extended as indicated at 20 so as to form a coaxial line output connection, the coaxial line being sealed in a vacuum tightmanner by an annular glass window 21.

Instead of employing a plurality of apertures 12, energy can be transferred from the cavity 1 via an annular gap 22 as shown in Figure 3 and the degree of coupling between the cavity 1 and the coaxial line 13 can be controlled by the provision of an annular diaphragm 23. Alternatively, as shown in Figure 4, a quarter wavelength transformer 24 may be employed between the cavity 1 and the coaxial line.

In the arrangement shown in Figures and 6 of the drawings, instead of employing the coaxial line as shown in Figure l a waveguide 25 is employed surrounding the cavity 1, energy being transferred from the cavity 1 to the waveguide 25 via an odd plurality of apertures 26 uniformly arranged around the outer wall of the cavity 1 as shown. In this arrangement the apertures 26 should be arranged one guide wavelength apart due to phase considerations. The outlet from the waveguide 25 is indicated at 27 in Figure 6 and the end of the waveguide adjacent the outlet end is tapered as indicated at 28, so as to avoid constricting the outlet end. The spacing between the coupling apertures 26 may be controlled to some extent by suitably choosing the longer dimension of the waveguide cross-section, thus varying the guide wavelength.

The constructions above-described can be applied to electron discharge devices in which a pair of cavity resonators are employed arranged concentrically with one another, as shown in Figure 7. In this embodiment the two concentrically arranged cavity resonators are indicated at 29 and 30 and the electrons emanating from the cathode 4 become velocity modulated on passing through the resonator 29 and become charge density modulated in the drift space between the resonator 29 and the resonator 30, the charge density modulated electron beam then passing through the resonator 30, where energy is abstracted from the beam. Surrounding the resonator 30 is a collecting electrode 31. The two resonators 29 and 30 may be coupled together for the inter-change of energy by means of energy transferring means including a plurality of apertures 32 in the outer wall of the cavity 29 and a plurality of apertures 33 in the inner wall of the cavity 30, these apertures being uniformly disposed about the cavities, and being enclosed by a pair of diaphragms 34 connected between the outer wall of the cavity 29 and the inner wall of the cavity 30', as shown. Energy is abstracted from the cavity 30 in any of the manners described with reference to Figures 1 to 6 as above described. Due to the uniform arrangement of energy transferring means both between the cavities 29 and 30 and between the cavity 30 and the output connection, the possibility of the cavities resonating in unwanted modes'is substantially avoided.

The invention can also be applied to electron discharge devices employing hollow cylindrical 'beams of electrons. Figure 8 of the drawings illustrates a construction of device employing such a hollow beam and in which two cavity resonators are employed. As shown in Figure 8, the two cavity resonators are indicated at 35 and 36 and a ring-shaped cathode 37 is employed which serves to emit a hollow cylindrical beam of electrons which passes in turn through the annular gaps in the cavities 35 and 36, and to an annular collecting electrode as. Energy is transferred from the cavity 36 in any of the manners described with reference to Figures 1 to 6. The cavities 35 and 36 may be coupled by the apertures 32 and 33 which are enclosed by spaced cylindrical walls 34. Figure 9 of the drawings illustrates a modification'of the arrangement shown in Figure 8 in which the output connection indicated at 39 is provided adjacent the inner periphery of the cavity 36, the output connection being fed via energy transferring means in the form of a'plurality of apertures or an annular slot as above described and around the inner periphery of the cavity. In this arrangement an input connection 40 is shown for'feeding the cavity 35, this input connection also being coupled to the inner periphery of the cavity 35 and feeding the cavity via a plurality of apertures or an annular slot as above described. Figure 10 of the drawings illustrates a modification of the arrangement shown in Figures 8 and 9 in which one of the cavities is surrounded by a waveguide 41, energy being transferred from the cavity 36 to the waveguide 41 via a plurality of uniformly disposed apertures 42.

Devices shown in Figures 7, 8, 9 and 10 with coupling between the two cavities will operate as oscillation generators, although if the devices are intended to be employed as amplifiers the coupling between the two cavities will be omitted. If desired, where a coupling between a pair of resonators is employed, such as in the devices shown in Figures 7 and 8, then a conventional form of coupling may be employed, although it is preferable to employ a coupling in accordance with the invention between the two resonators, as this further reduces the possibilities of unwanted modes being set up. Furthermore, where the devices shown in Figures 7 and 8 are intended to be operated as amplifiers, then an input connection will be required to the cavity 29 or 35, in which case the input connection comprises uniformly disposed energy transferring means such as is shown in Figure 9 so as further to reduce the possibility of unwanted modes being set up when energy is fed to the cavity 29 or 35.

What we claim is:

1. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having at least one opening other than an electron beam passing opening separate from said openings forming said annular gap and spaced from and symmetrically disposed about the axis of said resonator and constituting energy transferring means which transfers energy externally of the resonator to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode.

2. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having at least one opening separate from said openings forming said annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode, and an outer tubular conductor surrounding the outer boundary of said energy transferring means and an inner conductor arranged around the inner boundary of said energy transferring means said outer and inner conductors forming a coaxial line.

3. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having at least one opening separate from said openings forming said annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode, and a tapered outer tubular conductor surrounding the outer boundary of said energy transferring means and a tapered inner conductor arranged around the inner boundary of said energy transferring means said outer and inner conductors forming a coaxial line.

4. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a

cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having at least one opening separate from said openings forming said annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode, and a waveguide symmetrically disposed about the axis of said resonator and communicating with said energy transferring means.

5. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a plurality of openings other than electron beam passing openings separate from said openings forming said annular gap and spaced from and symmetrically disposed about the axis of said resonator and constituting energy transferring means which transfers energy externally of the resonator to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode.

6. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a plurality of openings separate from said openings forming said annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode, and an outer tubular conductor surrounding the outer boundary of said transferring means and an inner conductor arranged around the inner boundary of said energy transferring means said outer and inner conductors forming a coaxial line.

7. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a plurality of openings separate from said openings forming said annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform load ing of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode and a tapered outer tubular conductor surrounding the outer boundary of said energy transferring means and a tapered inner conductor arranged around the inner boundary of said energy transferring means said outer and inner conductors forming a coaxial line.

8. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annual opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a plurality of openings separate from said openings forming said annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode and a waveguide symmetrically disposed about the axis of said resonator and communicating with said plurality of openings.

9. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a further annular gap separate from said openings forming said first-mentioned annular gap and symmetrically disposed about the axis of said resonator and constitutingenergy transferring means to provide substan tially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode.

10. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a further annular gap separate from said openings forming said first-mentioned annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode and an outer tubular conductor surrounding the outer boundary of said transferring means and an inner conductor arranged around the inner boundary of said energy transferring means said outer and inner conductors forming a coaxial line.

11. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a further annular gap separate from said openings forming said first-mentioned annular gap and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode and a tapered outer tubular conductor surrounding the outer boundary of said energy transferring means and a tapered inner conductor arranged around the inner boundary of said energy transferring means said outer and inner conductors forming a coaxial line.

12. An electron discharge device comprising a toroidal cavity resonator, said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gap, said resonator having a further annular gap other than an electron beam passing gap separate from said openings forming said firstmentioned annular gap and spaced from and symmetrically'disposed about the axis of said resonator and constituting energy transferring means which transfers energy externally of the resonator to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode and a waveguide symmetrically disposed about the axis of said resonator and communicating with said further annular gap.

13. An electron discharge device comprising a toroidal cavity resonator said resonator having two annular oppositely disposed walls each formed with an annular opening, said openings together forming an annular gap, a further toroidal cavity resonator said further resonator having two annular oppositely disposed walls each formed with an annular opening, said latter openings together formingan annular gap, a cathode for generating a beam of electrons which is adapted to pass through said annular gaps, each resonator having at least one opening separate from said openings forming said annular gaps and symmetrically disposed about the axes of said resonators and constituting an'energy transferring means for transferring energy from one resonator to the other and to provide a substantially uniform loading of said resonators and thereby to reduce the liability of said resonators to resonate in an unwanted mode.

14. An electron discharge device according to claim 13 wherein one of said resonators is formed with at least one further opening constituting further energy transferring means symmetrically disposed about the axis of its associated resonator to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode.

15. An electron discharge device according to claim 14 wherein there is provided an outer tubular conductor surrounding the outer boundary of said further opening and an inner conductor surrounding the inner boundary of said inner opening said outer and inner conductors forming a coaxial line.

16. An electron discharge device according to claim 14 wherein a tapered outer tubular conductor is provided surrounding the outer boundary of said further opening 8 and a-tapered inner conductor is provided surrounding the inner'boundary of said further opening, said outer and innerconductors forming a coaxial line.

17. An electron discharge device comprising a toroidal cavity resonator said resonator having two annular oppositely disposed walls each formed withan annular opening said openings together forming an annular gap, an annular cathode for generating a hollow annular beam of electrons which is adapted to pass through said annular gap said resonator having at least one opening other than an electron beam passing opening separate from said openings forming said annular gap and spaced from and symmetrically disposed about the axis of said resonator and constituting energy transferring means which transfers energy externally of the resonator to provide substantially uniform loading of said resonator and thereby to reduce the-liability of said resonator to oscillate in an unwanted mode.

18. An electron dischargedevice comprisinga toroidal cavity resonator said resonator having two annular oppositely disposed walls each formed with an annular opening said openings together forming an annular gap, an annular cathode for generating a sheet-like beam of electrons which isadapted to pass through said annular gap said resonator having at least one opening other than an electron beam passing opening separate from said openings forming said annular gap and spaced from and symmetrically disposed about the axis of said resonator and constituting energy transferring means to provide substantially uniform loading of said resonator and thereby to reduce the liability of said resonator to oscillate in an unwanted mode.

References Cited in the file of this patent UNITED STATES PATENTS 2,259,690 Hansen Oct. 21, 1941 2,392,380 Varian Jan. 8, 1946 2,394,008 Pierce Feb. 5, 1946 2,466,063 Varian Apr. 5, 1949 2,506,752 Truel May 9, 1950 2,653,273 Sloan Sept. 22, 1953 2,667,598 Linder Jan. 26, 1954 

